This invention relates to an electrophotographic printing machine, and more particularly concerns an improved stapling apparatus for use therein.
In the process of electrophotographic printing, a photoconductive member is charged to a substantially uniform level so as to sensitize the surface thereof. Thereafter, the charged photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive surface discharges the charge selectively in the irradiated areas. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed by bringing a developer mix into contact therewith. In this manner, toner particles are attracted from the carrier granules of the developer mix to the latent image forming a toner powder image thereon. Thereafter, the toner powder image is transferred to the copy sheet and permanently affixed thereto. This general approach was originally disclosed by Carlson in U.S. Pat. No. 2,297,691, and has been further amplified and described by many related patents in the art.
On many occasions, it is highly desirable to reproduce a set of original documents as a plurality of sets of copies. This is generally achieved by employing a recirculating document handling system in association with the electrophotographic printing machine. The recirculating document handling system is positioned on the exposure platen of the printing machine to advance successive original documents thereto. Each original document disposed on the platen is exposed and, subsequently, reproduced. After being copied, the original document is returned to the stack of original documents so that it may be re-imaged for the next successive copying cycle. In this manner, collated sets of copies or booklets may be formed. Each booklet corresponds to a set of the original documents.
Frequently, the copy sheets of a specific booklet are stapled to one another. To this end, a stapling apparatus drives a plurality of staples through the sheets of the booklet. After the staple is driven through the set of copy sheets, the staple legs are clinched by either a passive or active clinching mechanism. In order to extend the range of set thickness, bypass clinching is frequently employed. In bypass clinching, the staple legs are bent into contact with the lowermost sheet of the booklet and are closely adjacent and overlapping one another. One of the major advantages of bypass clinching is that a single staple length may be employed for a wide range of differing thickness booklets. Active clinching systems employ clinching ears which pivot to bend the staple legs during the clinching operation. Hereinbefore, bypass clinching ears exhibited fundamental flaws which made them less desirable for use in an electrophotographic printing machine. For example, if the staple leg wandered when it was being driven through the booklet, jamming frequently occured between the clinching ears and the housing. In addition, the clinching ears were frequently dimensioned so that they could not accommodate substantial misalignment between the stapler head and clinching ears. This affected staple esthetics in that the staple rolled over and the legs spread on thin sheets.
Accordingly, it is a primary object of the present invention to improve the clinching mechanism of a stapling apparatus employed in an electrophotographic printing machine.